Originally Posted by
parabellum
Most long haul aircraft carry a body bag or two and should a pax die en route then it would be quite normal to place them, in the bag, in a toilet and lock the door so that other pax can't use it.
Every thing else relevant has been mentioned already, especially the risk of an unscheduled landing in a foreign country with a dead person on board.
If you land in the UK with a dead passenger on board then everyone has to remain on board until a doctor confirms that no foul play is suspected, police will attend and stand by any open doors until the aircraft is cleared.
Having landed a dead body into the UK I need to correct you, most airlines do NOT carry body bags, when we landed the passengers waited about 2 minutes before they could de plane a paramedic boarded along with a police officer, the former confirmed NO suspicious circumstances & passengers were allowed to disembark.